Method of refining alloys



States Patent Office" Patented Nov. 3, 1970 3,537,916 METHOD OF REFINING ALLOYS Roger David Butler, Kidlington, Ian Frederick Bowers,

Heatherton, Freeland, and Cedric Charles Edward Colley, Wheatley, England, assignors to Pressed Steel Fisher Limited, Cowley, Oxford, England, a corporation of Great Britain No Drawing. Filed Jan. 19, 1968, Ser. No. 699,024 Claims priority, application Great Britain, Jan. 25, 1967,

3,714/67; Mar. 8, 1967, 10,805/67 Int. Cl. C22f N10 US. Cl. 14811.5 3 Claims ABSTRACT OF THE- DISCLOSURE The structure of those eutectoid or near eutectoid alloys, such as zinc-aluminum, that retain a high temperature solid phase state after quenching from above the eutectoid temperature is refined by working the alloy in the solid phase high temperature state obtained after quenching from above the eutectoid temperature; accordingly, a zincaluminum eutectoid or near eutectoid alloy sheet having a refined structure is produced by continuously casting the alloy, quenching the continuously cast sheet and working prior to the transformation to the eutectoid or partly eutectoid state.

This invention relates to a method of refining the structure of those eutectoid or near eutectoid alloys that immediately after quenching from above the eutectoid temperature to ambient temperature retain the high temperature phase state during an incubation period prior to the start of a transformation period wherein the alloy transforms to the eutectoid or partly eutectoid state.

The object of this invention is to provide a method of refining the structure of such alloys.

According to the invention a method of refining the structure of such alloys includes the step of working the alloy during the incubation period.

By working is meant a process in which the alloy undergoes mechanical deformation such as, for example, rolling, forging, or drawing. 4

Preferably after working the alloy is cooled by, for example, immersing it in a cooling liquid to absorb the heat liberated by the transformation.

Conveniently, the alloy is cooled, after quenching, to a temperature below ambient whereby the incubation period is prolonged thereby giving more time for working the alloy.

According to a further aspect of the invention a method of producing a sheet of zinc-aluminum eutectoid or near eutectoid alloy having a refined structure, includes continuously casting the molten alloy on at least one roll, allowing the alloy to cool below the solidus temperature but above the temperature at which eutectoid transformation occurs, quenching to a temperature at least below 150 C., and rolling the sheet whilst it is in the a state to the required thickness.

Preferably the sheet is quenched to about ambient temperature. Quenching may be effected by spraying with or dipping into, a liquid, or by any means of effecting rapid cooling, such as to avoid the precipitation of the ,8 phase. Thus it will be understood that rolling is effected during the incubation period before transformation to the +5 two phase state.

In some cases the sheet may be maintained at a temperature between the solidus temperature and the temperature at which eutectoid transformation occurs for sufficient time to allow the structure of the sheet to be fully homogenised before quenching.

Embodiments of the invention will now be described solely by way of example:

EXAMPLE I A half inch diameter rod of zinc-aluminum alloy containing 78% by weight of Zinc was heated for 30 minutes in a furnace maintained at 350 C. so that transformation into the a phase was complete. The rod was quenched in water at ambient temperature and drawn during the incubation period which lasted for approximately 50 seconds at this temperature, to three eighths of an inch diameter through a circular draw die mounted on a rod drawing table. The rod was then immediately transferred into water at ambient temperature where, at the end of the incubation period, transformation to the two phase part eutectoid state occurred. After the transformation was complete, examination with an electron microscope showed that the eutectoid structure was finer than that of a comparative specimen that had not been cold worked by drawing prior to the transformation to the two phase part eutectoid state.

EXAMPLE II A specimen of zinc-aluminum alloy, containing 78% by weight of zinc was heated in a furnace maintained at 350 C. for 30 minutes so that transformation into the a phase was complete. The specimen was quenched in cold water and was then immediately cooled to a temperature of 10 C. The specimen was then immediately rolled to give a 50% reduction in cross-sectional area and rolling was completed within a period of approximately three minutes from quenching so that rolling had finished prior to the start of transformation from the single a phase to the a-l-fi two-phase eutectoid state. Immediately rolling was completed the specimen was placed in water at ambient temperature.

The specimen was allowed to warm up, and transformation to the two phase state was allowed to occur.

After the transformation was completed examination with an electron microscope showed that the structure of the alloy was finer than that of unprocessed alloys of the same composition.

EXAMPLE III A zinc-aluminum alloy containing 80% by weight of zinc was heated to a temperature of 550 C. The moltep alloy was fed into a well formed between two, two foot diameter steel rolls mounted in a common horizontal plane with a roll gap of about of an inch. The rolls were internally water-cooled and were so rotated in opposite directions that solidified material was drawn through the roll gap. solidification of the alloy occurred adjacent the cooled surfaces of the rolls such that the alloy was substantially solidified when it was drawn through the roll gap. 1

The substantially solidified sheet emerging from the roll gap was allowed to cool to 325 C. and was then sprayquenched to ambient temperature. The quenched sheet in the a state was then rolled to the required thickness between final-sizing rolls during the incubation period and prior to transformation to the a+13 two phase state.

EXAMPLE IV A substantially solidified sheet continuously cast as described in Example III was cooled and held at about 375 C. as it emerged from the roll gap to homogenise the structure, the sheet was then cooled to about 325 C., and was then rapidly cooled to ambient temperature by a spray quench. The sheet is then rolled to the required thickness.

3 EXAMPLE V A substantially solidified sheet continuously cast as described in Example III was maintained in contact with one of the rolls after it emerged from the roll gap in order to cool the sheet rapidly to ambient temperature. The sheet was then rolled in the a state during the incubation period, to the required thickness.

EXAMPLE VI 7 The same molten alloy described in Example III was cast on the surface of a single cooled roll from an orifice positioned in close proximity to the surface of the roll. When the metal in contact with the roll had at least partially solidified it was peeled from the surface of the roll.

The sheet peeled from the roll was subsequently treated as described inExample III or IV.

What we claim is:

1. A method of refining the structure of those zinc base eutectoid or near eutectoid superplastic alloys that imme diately after quenching from above the eutectoid temperature to ambient temperature retain the high temperature solid phase state during an incubation period prior to-thestart of a transformation period wherein the alloy transforms to at least a partly eutectoid state, which includes the step of working said alloy during said incubation period.

2. A method according to claim 1, which includes the step of extracting heat from said alloy during said transformation period.

3. A method of producing a sheet of a zinc-aluminum eutectoid or near eutectoid alloy having a refined structure which includes the steps of continuously casting said alloy on at least one roll, quenching said alloy and then rolling said alloy during said incubation period.

References Cited UNITED STATES PATENTS 3,340,101 9/1967 Fields et a1. 148-11.5

L. DEWAYNE RUTLEDGE, Primary Examiner W. W. STALLARD, Assistant Examiner 

